<template>
  <div class="pagination">

    <!-- 这里的pageNo - 1，代表当前页的上一页 -->
    <button :disabled='pageNo==1' @click="$emit('getPageNo',pageNo - 1)">上一页</button>
    <button v-if="startNumAndEndNum.start > 1" @click="$emit('getPageNo',1)" :class="{active: pageNo ==1}">1</button>
    <button  v-if="startNumAndEndNum.start > 2">···</button>
    
    <!--中间部分 -->
    <button v-for="(page,index) in startNumAndEndNum.end" :key="index" v-if="page >= startNumAndEndNum.start"  @click="$emit('getPageNo',page)" :class="{active: pageNo == page}">{{page}}</button>
    
    <!-- 下 -->
    <button v-if = "startNumAndEndNum.end < totalPage - 1">···</button>
    <button v-if='startNumAndEndNum.end < totalPage'  @click="$emit('getPageNo',totalPage)"  :class="{active: pageNo == totalPage}">{{totalPage}}</button>
    <button :disabled='pageNo==totalPage' @click="$emit('getPageNo',pageNo + 1)">下一页</button>

    <button style="margin-left: 30px">共 {{total}} 条</button>
  </div>
</template>

<script>
export default {
  name: "Pagination",
  // 父组件传递给字符串的数据：当前页、每一页展示多少条数据、数据总个数、连续页码数
  props:['pageNo','pageSize','total','continues'],

 computed: {
    // 总共有多少页
    totalPage(){
        //  向上取整    
        return Math.ceil(this.total/this.pageSize)
    },
    // 计算出连续的页码的起始数字与结束数字[连续页码数字最五页]
    startNumAndEndNum(){
        // 这里解构就可以不用每一个都this
        const {continues,pageNo,totalPage} = this
        // 先定义俩个变量存储起始数字与结束数字
        let start = 0,end = 0;
        // 连续页也大于总页数，比如连续页如果是5的话，总页数为4就会进入以下判断
        if(continues > totalPage){
            start =  1;
            end = totalPage;
        }else{
            // 正常现象【连续页码5，但是你的总页数一定是大于5的】
            // 当前页减去连续页的除2在向下取整的数
            // 起始数字
            start = pageNo - parseInt(continues/2)
            // 结束数字
            end = pageNo + parseInt(continues/2)
            // 把出现不正常的现象【start数字出现0|负数】纠正
            if(start < 1){
                start = 1;
                end = continues
            }
            // 把出现不正常的现象【end数字大于总页码】纠正
            if(end > totalPage){
                end = continues;
                start = totalPage - continues + 1

            }
        }
        return {start,end};
    }
 }
};
</script>

<style lang="less" scoped>
.pagination {
     text-align: center;
  button {
    margin: 0 5px;
    background-color: #f4f4f5;
    color: #606266;
    outline: none;
    border-radius: 2px;
    padding: 0 4px;
    vertical-align: top;
    display: inline-block;
    font-size: 13px;
    min-width: 35.5px;
    height: 28px;
    line-height: 28px;
    cursor: pointer;
    box-sizing: border-box;
    text-align: center;
    border: 0;

    &[disabled] {
      color: #c0c4cc;
      cursor: not-allowed;
    }

    &.active {
      cursor: not-allowed;
      background-color: #4090ff;
      color: #fff;
    }
  }
}

</style>